Step drill bit



FIG. 1 is a left side elevation view of a step drill bit embodying our new design;

FIG. 2 is a front elevation view thereof; and,

FIG. 3 is an enlarged top plan view thereof.

Portions of the step drill bit shown in broken lines form no part of the claimed design. 

CLAIM We claim the ornamental design for a step drill bit, as shown and described. 